The bicycle, serving as a traffic tool for daily use, not only is environment-friendly, but also is capable of building up body, and is thus favored by the public. With development of science and technology, more and more electronic equipment or safety equipment, such as a nightlight may be assembled on the bicycle, and accordingly a bicycle-mounted holder is produced, however, the bicycle-mounted holder commercially available at present cannot be buckled on a seat, handles, a helmet, a front fork or a rear fork freely, and when the handles are different in shape or size, the bicycle-mounted holder also needs to be replaced again. It thus can be seen that a holder which may be buckled on the seat, the handles, the helmet, the front fork, the rear fork or the like freely is urgent to be developed for the purpose of meeting the mounting requirements of different users or different equipment.